The implementation and improvement of telecommunications services with automatic voice output and voice transmission over a packet network is currently an important area of development in the field of switching technology.
Packet networks provide transmission capacities which are extensive in many ways and are already widely used for transmitting data. At present, increased efforts are being made to use the bandwidth made available by packet networks also for voice-based services. For example, work is being carried out on implementing the voice-based services over the Internet using the Internet Protocol (IP). In this context, the term voice over IP, abbreviated as VoIP, is often used.
The transmission of voice data over packet networks has the advantage of greater flexibility and a better use of the available transmission capacity than the conventional circuit-switched transmission of what are referred to as TDM (time division multiplexing) networks. Owing to the utilization of the capacity of the available packet networks, it is also assumed that the costs of voice-based services are lower than for circuit-switched transmission.
For the acceptance of voice-based services with data transmission over a packet network, it is important that the service features which are offered with voice transmission over a TDM network are also made available for transmission over a packet network.
For controlling voice connections with useful data transmission over a packet network, the BICC (bearer independent call control) protocol has been developed, and this protocol is described in the ITU-T standards Q.1901 and Q.1902.
Within the scope of data transmission using the BICC protocol, the useful data and the signaling information are frequently transmitted separately from one another. Within the scope of a link which is set up using the BICC protocol, the signaling information can be routed via a CMN (call mediation node). According to the ITU-T Q.1901, CMNs fulfill control functions without having direct access to the routing of the useful data, as is the case with SNs (service nodes). CMNs can optionally be used in BICC networks. A possible application of CMNs in the case of hierarchically structured switching is to control or direct the signaling information at higher switching levels from which there is no access to the useful data routing.
According to the standard (Q.1902.4, section 9.5.2 and Q.1901 section 10.2.2.4 a) and appendix III) it is not possible to create announcements or tones, i.e. IVR (interaction voice response) resources in a CMN. Reference is made only to the possibility of using a fault message (cause value) to bring about an interruption in the current state and to implement a link to IVR resources which are made available at another location—for example at an SN.